Simple fatty streak is the earliest lesion of
atherosclerosis, which eventually change to fibrous plaques resulting in
arterial occlusion, thereby producing overt clinical manifestations. With the
possible exception of the early fatty streaks the reversal of atherosclerotic
lesion does not occur even under most favourable conditions3.
Garlic, a widely distributed plant is used in
all parts of the world, not only as a spice and a food, but also as a popular
remedy for some common illness. Its importance was recognized several thousand
years ago and was regarded as a remedy for a variety of ailments, including
heart, diabetes and tumours5. As a natural product, garlic has become the focus for the
promising protective effect against hyperlipidaemia and atherolscerosis6,7. However some authors have failed to confirm
the effect of garlic on blood lipid and atherosclerosis in
hyperlipoproteinaemic individuals8.
In view of this controversial effect of garlic
on serum lipid, the present study was planned to re-evaluate the role of garlic
in the prevention of hyperlipidaemia.
Materials and Methods
Eighteen healthy New Zealand white rabbits of
either sex, weighing between 1 to 2 kgm were selected for this study. The
animals were kept on basal laboratory diet, with fresh food, water and in a
good hygienic condition for 2 weeks before commencing the experiment to make
adaptation with environment. The duration of the experiment was 10 weeks. The animals were divided into three
batches of 6 depending on diet and drugs as follows.
1. Normal
Control (6): On basal laboratory
diet containing wheat and wheat brans (30% each), maize, Jill cake, kheshari
(10% each), soybean oil 4%, molasses 1% with skimmed milk powder, vitamin
mixtures and minerals in appropriate proportions. The diet was prepared
according to the formula followed by the International center for Diarrhoeal
Disease Research, Bangladesh (ICDDRB).
2. Atherosclerotic
Control (6): On atherogenic diet containing basal laboratory diet+ 6%
coconut oil +1% cholesterol. The atherogenic diet was prepared by dissolving
powdered cholesterol in heated coconut oil. It was then mixed with pellets of
basal laboratory diet and the mixture was agitated to have a homogenous
distribution of cholesterol and coconut oil in the pellets.
3. Garlic
treated (6): On atherogenic diet
+10ml/kg freshly prepared aqueous extract of
garlic daily. The bulbs of Garlic were sliced into pieces and
homogenized with cold distilled water at a proportion of 1:3 by weight. The
filtered mixture was centrifuged at 3000rpm for 15 minutes. The supernatant
fluid was used for treating the rabbits. The procedure of preparation and the
doses of aqueous extract of garlic were chosen from Augusti and Methew9.
To see the antilipidaemic effects of garlic,
biochemical parameters were used. Serum cholesterol, triglycerides, low-density
lipoprotein and high-density lipoprotein were estimated at the beginning and on
the day of sacrifice for each animal of each batch. Comparative studies were
made between the results among different batches of rabbits.
Results
After 8 weeks of atherogenic diet feeding, the
rabbits developed small nodular skin lesions mostly in both ears. The initial
lipid levels in different batches of rabbits were close to each other. At the
end of the experiment, the serum lipid level of the cholesterol fed animals
increased many folds to that of the initial levels except in the normal control
batch (Table 1). Serum cholesterol level increased maximally to about 14 times
the initial level and showed markedly higher level of cholesterol. The increase
of serum triglycerides was relatively lower as compared to serum cholesterol
and LDL level. The mean final serum HDL levels were less than the mean initial
ones in all batches of rabbits.
Table – I: Serum lipid levels in different batches of rabbits at the
beginning and end of the experiment
|
Batch
|
Serum lipids
|
Serum
lipid (mg/dl) Mean ± SD
Initial Final
|
Final
serum lipid as a Percentage of initial level (%) Mean±SD
|
|
1. Normal control(n=6)
|
Chol
|
107.55±27.01
|
126.64±22.75
|
120.03±17.67
|
|
|
TG
|
109.63±16.48
|
131.44±30.29
|
121.87±34.71
|
|
|
LDL
|
50.02±27.61
|
66.11±25.81
|
150.29±71.76
|
|
|
HDL
|
35.61±5.77
|
34.24±3.93
|
97.38±12.68
|
|
2. Ath control (n=6)
|
Chol
|
102.30±19.48
|
1461.24±527.85
|
1400.72±335.60
|
|
|
TG
|
104.28±29.71
|
328.30±58.93
|
339.04±105.46
|
|
|
LDL
|
45.05±21.81
|
1372.45±533.95
|
3201.15±700.37
|
|
|
HDL
|
36.40±3.63
|
23.17±4.01
|
64.59±15.41
|
|
3.Garlic treated (n=6)
|
Chol
|
97.55±22.31
|
496.94±261.48
|
532.58±273.02
|
|
|
TG
|
109.68±11.98
|
177.06±69.46
|
163.91±75.73
|
|
|
LDL
|
43.02±22.52
|
431.56±254.50
|
1482.63±1355.55
|
|
|
HDL
|
32.60±5.96
|
29.97±6.98
|
92.36±15.89
|
Batch 2
vs 1 p<0.001 for Chol, TG, LDL, HDL
Batch
2 vs 2 p<0.001 for Chol, TG, p<0.05 for LDL & HDL
Serum cholesterol (Table 1)
The mean final serum cholesterol level in the
atheroscloretic control batch was 12 times more than that in the normal control
ones. In the normal control rabbits the mean of the final serum cholesterol
levels as percentage of the initial ones was 120.03±17.67mg/dl and that of the atherosclerotic
control ones was 1400.72±335.60 mg/dl. A very
significantly higher difference (p<.001) was found when the two batches of rabbits were compared
statistically for the final serum cholesterol levels expressed as a percentage
of the corresponding initial level.
The mean final serum cholesterol in the garlic
treated rabbits was 496.94 ±261.48
mg/dl, which was about 5 times higher than that of the corresponding mean
initial level (97.55 ± 22.31 mg/dl). The mean of
the final levels expressed as percentages of the corresponding initial levels
(532.58 ±273.02 mg/dl) was very
significantly lower (p<.001) than that
in the atherosclerotic control ones (1400.72± 335.60 mg/dl).
Serum triglycerides (Table 1)
The mean final of serum
triglycerides and that was expressed as percentage of the corresponding initial
levels in the normal control batch was 131.44 ± 30.29 mg/dl and 121.87±34.71
mg/dl respectively. The mean final serum triglycerides level in the
atherosclerotic control batch was 328.30±58.93 mg/dl, almost
double than the mean final value in the normal control batch. The mean of the
final triglycerides level expressed as percentages of the corresponding initial
ones in this batch (339.04±105.46 mg/dl) was very significantly
higher (p<.001) than that in the normal control ones.
The mean final level of serum triglycerides in
the garlic treated rabbits was 177.06±69.46
mg/dl and the mean of the final levels expressed as percentages of the
corresponding initial levels (163.91±75.73
mg/dl) was very significantly lower (p<.001) than that in the atherosclerotic control ones (339.04±105.46 mg/dl).
Low-density lipoprotein (Table 1)
In normal control batch, the mean final serum
level and the levels expressed as percentages of the corresponding initial
levels was 66.11±25.81 mg/dl and 150.29±71.76 mg/dl respectively. The mean final serum LDL level in the
atherosclerotic control batch (1372.45±533.95
mg/dl) was about 20 times than that of the mean final LDL level in the normal
control ones (66.11±25.81 mg/dl). The mean of
the final serum LDL levels expressed as percentages of the corresponding
initial levels in this batch (3201.15±700.37
mg/dl) was very significantly higher (p<.001) than in the normal control batch (150.29±71.76 mg/dl). In the garlic treated batch, the mean final LDL level
was 431.56 ±254.50 mg/dl and the mean of the final serum
LDL levels expressed as percentages of the corresponding initial levels
(1862.63±1355.55 mg/dl) was significantly lower (p<.05) than in the atherosclerotic control ones (3201.15 ±700.37 mg/dl).
High-density lipoprotein (Table 1)
The mean initial and
final serum HDL levels in the normal control batch were 35.61 ±
5.77 mg/dl and 34.24 ± 3.93 mg/dl respectively. The mean final HDL level in the
atherosclerotic control batch (23.17 ± 4.01 mg/dl) was about
30% lower than the mean final HDL level in the normal control ones (34.24 ±
3.93 mg/dl). The mean of the final serum HDL levels expressed as percentages of
the corresponding initial levels in this batch (64.59 ±
15.41 mg/dl) was very significantly lower than (p< .001) then the normal
control batch (97.38 ±12.68 mg/dl).
In the garlic treated rabbits fed on atherogenic diet the mean final HDL level
(29.97±6.98 mg/dl) and that the mean of the final serum HDL levels
expressed as percentages of the corresponding initial levels in this batch
(92.36 ± 15.89 mg/dl) was significantly higher (p<.05)
than that in the atherosclerotic control ones (64.59 ±
15.41 mg/dl).
Statistical comparison of the final serum
lipid (as percentage of the corresponding initial level) between different
batches of rabbits were carried out through unpaired ‘t’ test of significance
of difference.
Discussion
The effect of atherogenic diet when compared
to the outcome of the basal laboratory diet feeding could be assessed by
comparing the findings in the atherosclerotic control rabbits with those in the
normal control ones. Statistically highly significant difference between the
two batches of rabbits could be detected in all biochemical parameters. The
mean final serum cholesterol as well as mean of the final levels expressed as
percentages of the corresponding initial levels in the atherosclerotic control
rabbits increased by about 10 times than that in the normal control ones.
Bordia et al.6 and Sainani et al.10 reported about 8 times higher level of serum
cholesterol in the atherosclerotic control batch than that in the normal
control ones by feeding 0.5 gm of cholesterol to male albino rabbits for 8 and
12 weeks respectively. Hollander et.al.11 and Jain12 also
demonstrated the same results. The final serum triglycerides and the mean of
the final levels expressed as percentages of the corresponding initial levels
were more than 2.5 times and about 65% respectively higher in the
atherosclerotic control rabbits than that in the normal control ones. Similar
higher levels have also been reported by Sainani et.al.10. The mean final serum LDL level in the
atherosclerotic control rabbits increased by almost 20 times than that in the
normal controls ones. Bordia et.al.6 Sannani et.al.10 studied
on the male rabbits by feeding 0.5 gm of cholesterol daily and found higher LDL
level. The mean final serum HDL level in the atherosclerotic control rabbits
was about 30% lower than that in the normal control ones. Similar reduction was
reported by Sainani et.al.10 by feeding 0.5 gm of
cholesterol to rabbits for 12 weeks.
In the garlic treated rabbits, the mean final
cholesterol level was decreased by 65% than that in the atherosclerotic
controls ones. Jain12 (1976) and Sainani et.al.10 (1979)
in the cholesterol fed rabbits treated with garlic for 12 weeks have reported
similar reduction. 10% reduction of serum cholesterol after 3 hours in a
healthy individual by simultaneous feeding of 50 gm garlic juice with 100
butter and 4 pieces of bread have been observed by Bordia et al.4 Reduction of serum cholesterol has also been
reported by Huq13 by intragastric administration of garlic in
cholesterol fed rats for 10 weeks.
The mean final serum triglycerides level in
the garlic treated rabbits was reduced by 45% than that in the atherosclerotic
control rabbits. Bordia et al.6 and Sainani et al.10 also
demonstrated similar results. Both found more reduction of serum triglycerides
in the garlic treated rabbits. More than 25% reduction has been demonstrated by
Zacharias et al.14 in sucrose fed atherogenic rabbits treated
with 10 ml/kg of aqueous extract of garlic for 8 weeks.
The mean final serum LDL in the garlic treated
rabbits was about 70% lower than that in the atherosclerotic control ones.
Bordia et al.6 and Sainani et al.10 have
observed about 20% reduction of serum of serum LDL level in a similar study.
40% reduction in the cholesterol fed rats treated with aqueous extract of
garlic for 10 weeks was found by Huq13.
In the present study, the mean final serum HDL level in the garlic
treated rabbits was increased by about 25% than that in the atherosclerotic
control ones. Similar results were also reported by Bordia et al.6 and Sainani et al.10. Both
observed quite higher levels of serum HDL in the cholesterol fed rabbits
treated with garlic. Huq13 found
serum HDL level increased by 30% in the garlic treated rats in comparison to
rats fed on cholesterol diet only.
Conclusion
The untreated rabbits on atherogenic diet
showed significantly worse lipidaemic status than the normal control ones as
evident in higher serum cholesterol, triglycerides and LDL, with lower serum
HDL level. On the other hand rabbits on atherogenic diet treated with garlic
showed better lipidaemic status.This was apparent from significant difference
between the two.
When there is a worldwide extensive search for
effective, easily available and economically preventive agents against one of
the deadliest killer disease–atherosclerosis, the present study has
demonstrated that garlic may have an antilipidaemic role against the
pathogenesis of atherosclerosis. Various authors have reported similar
antilipidaemic property of garlic.
Acknowledgment
The authors are grateful to Dr. Khondaker
Manzare Shamim, Professor & Chairman, Department of Anatomy, Bangabandhu
Sheikh Mujib Medical University, for his continuous support and valuable
suggestions regarding this study.
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